The present invention relates to a load weighing apparatus mounted on a vehicle such as a lorry or a truck or the like, for weighing a weight of a load.
Various apparatuses have been proposed as a weighing apparatus of the kind referred to above. A representative one of the apparatuses will be described hereunder.
(1) A weighing apparatus disclosed in Japanese Utility Model Publication No. 60-23687 comprises a pair of strain detectors of magneto-striction type which are mounted respectively on an upper surface and a lower surface of an axle, for detecting a compressive force on the upper surface and a tensile force on the lower surface, respectively, due to flexure of the axle. Detecting values of the compressive and tensile forces are added to each other to detect flexure of the axle without occurring of errors due to a change in temperature.
(2) A weighing apparatus disclosed in Japanese Utility Model Laid-Open No. 61-144435 comprises a load meter which is composed of a display element to which a mark indicating propriety or suitability of a load is applied, and an indicating element fixedly mounted on a body frame and which is movable along the mark on the display element in accordance with deflection of a suspension spring to indicate suitability of the load.
(3) A weighing apparatus disclosed in Japanese Patent Laid-Open No. 62-274223 disclosed that, in a vehicle such as a wheel loader or the like in which a load carrying section is movable vertically by a hydraulic cylinder, hydraulic pressures of the hydraulic cylinder before and after the load carrying section reaches a predetermined height position are sampled at predetermined time intervals and predetermined frequency numbers. A mean value of hydraulic data of these sampled hydraulic pressures is computed. The weight of the load on the load carrying section is equivalent to the hydraulic mean value.
(4) A weighing apparatus disclosed in Japanese Utility Model Laid-Open No. 61-14333 comprises a strain sensor which is mounted on a body frame. Flexure of the body frame at the time a load on a load-carrying platform is loaded and unloaded is correlated to that load. Thus, monitoring of the loading in view of a loading limit with respect to the vehicle is made possible.
Of the proposals disclosed respectively in the above-described publications, (1) is difficult implement in practical use because the measured values vary due to the permanent strain or flexure of the axle and due to material hysteresis. Further, (2) is also difficult to implement in practical use, because displacement hysteresis is large due to the fact that a characteristic of a spring displacement with respect to the load of the spring is different for every vehicle. Furthermore, (3) is applicable only to a vehicle such as a wheel loader having a hydraulic cylinder and is unsuitable for those vehicles not having a hydraulic cylinder. Moreover, (4) is impossible into practical use in measurement, because of permanent strain and hysteresis of the material of the body frame.